Electronic article surveillance (EAS) systems are used to control inventory and to prevent or deter theft or unauthorized removal of articles from a controlled area. The system establishes an electromagnetic field or “interrogation zone” that defines a surveillance zone (typically entrances and/or exits in retail stores) encompassing the controlled area. The articles to be protected are tagged with an EAS security tag. Tags are designed to interact with the field in the interrogation zone. The presence of a tag in the interrogation zone is detected by system receivers and appropriate action is taken. In most cases, the appropriate action includes the activation of an alarm.
EAS security tags may be affixed to any article, such as, for example, an article of merchandise, product, case, pallet, container, and the like, to be protected, monitored, retained, sold, inventoried, or otherwise controlled or distributed in some manner. The tag includes a sensor element adapted to interact with the electromagnetic field in the interrogation zone. In operation, an EAS system transmitter interrogates the tag by radiating a first signal at the tag's tuned resonant frequency. Some tags also respond to a second radiated field that is outside of the tag's tuned resonant frequency. The interaction of the first and/or second fields with the sensor element causes a change in the tag's characteristics that establishes the presence of an additional detection signal in the interrogation zone. The generation of harmonic frequencies, the generation of mixing side bands, or the re-radiation of the first signal modulated by the second signal, among other effects. Accordingly, if an article tagged with an EAS security tag traverses the interrogation zone, the EAS system recognizes the detection signal as an unauthorized presence of the article in the controlled area and may activate an alarm under certain circumstances, for example.
Radio frequency identification (RFID) utilizes interrogation and reply frequencies in the radio frequency (RF) band to perform electronic article identification (EAI) functions. An RFID tag is attached to an article to be identified. The RFID tag responds to an RF interrogation signal and provides the identification information in the form of an RF response signal. The identification information may comprise article identification information, pricing information, inventory control, and can receive and store information such as the date and place of sale, sales price, and article manufacturing authenticity information, for example. RFID tags comprise an integrated circuit (IC) and an antenna connected thereto. The IC may comprise a variety of architectures and the item identification code may be stored in a variety of code formats.
A transceiver and an RFID tag form an RFID system and communicate with each other over a wireless RF communication channel. The transceiver may comprise a hardware device to interrogate the RFID tag and initiate reading the article identification code. The transceiver may comprise an RFID transceiver adapted to communicate (e.g., read and write) information with the RFID tag. In operation, the transceiver sends a request for identification information to the RFID tag over the wireless RF communication channel and the RFID tag responds accordingly.
Conventional RFID tags, however, are typically not well suited to EAS applications because of its limited detection range due to the threshold effects. Presently, to obtain EAS and electronic article interrogation (EAI) functionality, EAS tags and RFID tags both are usually attached to an article if identification and protection of the article are desired. In some applications, RFID and EAS functions may be integrated within the same tag housing. The RFID and EAS functions, however, are usually electrically separate, discrete functions that are co-located within one enclosure.
It is sometimes desirable to have the EAS and RFID functionality present in the same tag housing. In some implementations, an RFID IC may include EAS as an auxiliary function. The combined EAS and RFID functions may be accomplished by physically packaging separate RFID and EAS tags together in a single housing. In some implementations, an RFID tag may be modified to simulate an EAS function by sending special codes when a reader interrogates the RFID tag. Physically packaging two separate RFID and EAS tags in a single housing, however, may be expensive because it may require two separate devices, a large bulky package, and the interaction between the two tags may degrade the detection range of both the RFID and the EAS functions. Using the RFID function with special codes to simulate the EAS function also is inferior. Typically an RFID IC requires a turn-on voltage of 1.3 volts or greater in order to operate. This turn-on voltage threshold requirement may limit the overall detection range if the interrogation signal received by the RFID is not sufficient to overcome the turn-on voltage threshold in order to provide an adequate amount of power to the IC.